The present invention relates to rotary electric motors, more particularly to winding circuit configurations for motors having a plurality of phases and the control of a multiphase motor using a minimum number of control states.
The above-identified copending patent applications describe the challenges of developing efficient electric motor drives for vehicles, as a viable alternative to combustion engines. Electronically controlled pulsed energization of windings of motors offers the prospect of more flexible management of motor characteristics. By control of pulse width, duty cycle, and switched application of a battery source to appropriate stator windings, superior functional versatility can be achieved. In many motor applications, a vehicle drive environment is but one example, it is highly desirable to attain smooth operation over a wide speed range, while maintaining a high torque output capability and conserving the power source.
Motor structural arrangements described in the identified copending applications contribute to these objectives. Electromagnet core segments may be configured as isolated magnetically permeable structures in an annular ring to provide increased flux concentration. Isolation of the electromagnet core segments permits individual concentration of flux in the magnetic cores, with a minimum of flux loss or deleterious transformer interference effects with other electromagnet members.
FIG. 1 is an exemplary view showing rotor and stator elements of a motor such as disclosed in the copending application Ser. No. 09/826,422, the disclosure of which has been incorporated herein. Rotor member 10 is an annular ring structure having permanent magnets 12 substantially evenly distributed along cylindrical back plate 14. The permanent magnets are rotor poles that alternate in magnetic polarity along the inner periphery of the annular ring. The back plate may comprise magnetically permeable material that serves as a magnetic return path between adjacent permanent magnetic poles 12. The rotor surrounds a stator member 20, the rotor and stator members being separated by an annular radial air gap. Stator 20 comprises a plurality of electromagnet core segments of uniform construction that are evenly distributed along the air gap. Each core segment comprises a generally u-shaped magnetic structure 24 that forms two poles having surfaces 26 facing the air gap. The legs of the pole pairs are wound with windings 28. Alternatively, the core segment may be constructed to accommodate a single winding formed on a portion linking the pole pair. Each stator electromagnet core structure is separate, and magnetically isolated, from adjacent stator core elements. The stator elements 24 are secured to a non magnetically permeable support structure (not illustrated), thereby forming an annular ring configuration. This configuration eliminates emanation of stray transformer flux effects from adjacent stator pole groups.
The above-identified application Ser. No. 10/173,610 describes motor control strategies contemplated for precise controlled performance for various applications of such motors. While typical control systems assume uniformity of parameter values over the entire motor, it is recognized in that application that provision of independent structural elements may cause variance of circuit parameters, such as phase resistance, phase self-inductance and the like, among the various stator elements. Motor control thus involves the fusion of nonlinear feedforward compensation coupled with current feedback elements. Each stator core segment is individually controlled as a separate phase, each set of phase windings energized in response to control signals generated by a controller in accordance with the set of control parameters associated with the stator phase component for the phase winding energized. In the exemplified seven phase motor illustrated, active control is required individually for all seven states.
Control according to application Ser. No. 10/173,610 is illustrated in FIGS. 2 and 3. The stator phase windings are switchably energized by driving current supplied from d-c power source 40 via electronic switch sets 42. The switch sets are coupled to controller 44 via gate drivers 46. Controller 44 has one or more user inputs and a plurality of inputs for motor conditions sensed during operation. Current in each phase winding is sensed by a respective one of a plurality of current sensors 48 whose outputs are provided to controller 44. The controller may have a plurality of inputs for this purpose or, in the alternative, signals from the current sensors may be multiplexed and connected to a single controller input. Rotor position sensor 46 is connected to another input of controller 44 to provide position signals thereto. The output of the position sensor is also applied to speed approximator 50, which converts the position signals to speed signals to be applied to another input of controller 44.
The sequence controller may comprise a microprocessor or equivalent microcontroller, such as Texas Instrument digital signal processor TMS320LF2407APG. The switch sets may comprise a plurality of MOSFET H-Bridges, such as International Rectifier IRFIZ48N-ND. The gate driver may comprise Intersil MOSFET gate driver HIP4082IB. The position sensor may comprise any known sensing means, such as a Hall effect devices (Allegro Microsystems 92B5308), giant magneto resistive (GMR) sensors, capacitive rotary sensors, reed switches, pulse wire sensors including amorphous sensors, resolvers, optical sensors and the like. Hall effect current sensors, such as F. W. Bell SM-15, may be utilized for currents sensors 48. The speed detector 50 provides an approximation of the time derivative of the sensed position signals.
FIG. 3 is a partial circuit diagram of a switch set and driver for an individual stator core segment winding. Stator phase winding 28 is connected in a bridge circuit of four FETs. Any of various known electronic switching elements may be used for directing driving current in the appropriate direction to stator winding 28 such as, for example, bipolar transistors. FET 53 and FET 55 are connected in series across the power source, as are FET 54 and FET 56. Stator winding 28 is connected between the connection nodes of the two series FET circuits. Gate driver 46 is responsive to control signals received from the sequence controller 44 to apply activation signals to the gate terminals of the FETs. FETs 53 and 56 are concurrently activated for motor current flow in one direction. For current flow in the reverse direction, FETs 54 and 55 are concurrently activated. Gate driver 46 alternatively may be integrated in sequence controller 44.
The particular circuitry shown and described above is merely representative of various alternative motor energization circuitry. However, each phase has associated switching and driver circuitry that permits active control of each phase state. For motors having a large number of phases, the duplication of such circuitry for each phase and the increased complexity of circuit real estate and functionality becomes expensive and burdensome. The need thus exists for effective control of a motor having a large number of phases while reducing the number or controllable states.
The present invention fulfills this need, while maintaining the benefits of the separated and ferromagnetically isolated individual stator core element configurations such as disclosed in the copending applications. A reduced number of controllable states is achieved while retaining a high degree of precision controllability.
Advantages are achieved with a multiphase brushless permanent magnet motor having a stator provided with at least one winding for each phase, the windings permanently connected to each other at a plurality of junctions. A power source is coupled, via controlled motor energization circuitry, to a plurality of terminals connected to respective junctions, the number of which terminals is fewer than the number of motor phases and, thus, the number of junctions. The motor energization circuitry is appropriately controlled by a central processor. Thus duplication of identical energization circuitry for each phase is avoided.
Such an arrangement can be obtained by configuring a first group of windings in a delta connected configuration, with adjacent windings of the configuration joined at a respective one of said junctions, and a second group of windings connected in a wye configuration, end points of the wye configuration joined to respective ones of said junctions. An end point of the wye configuration may be joined to a junction that is not directly connected to a terminal. As the invention is applicable to motors of various numbers of phases, the number of phase windings of the first group and second group is also variable. In a preferred illustrated embodiment, the motor comprises seven phases, the delta configuration comprises five of the phase windings with five junction points, the wye configuration comprises two of the phase windings, one leg of the wye being directly connected between one of the junctions and a center node to which the other wye windings are joined. In that embodiment, only four of the junction points are directly connected to respective power supply terminals. A first resistance element may be connected across the two phase windings of the wye configuration and a second resistance element may be connected between the center node of the wye configuration and one of the junctions.
The present invention is advantageous in a motor in which the stator further comprises a plurality of ferromagnetic core segments ferromagnetically isolated from each other, each core segment having a respective phase winding formed thereon. Each core segment comprises a plurality of poles, each pole facing the rotor across a radial air gap. The number of phases is equal to the number of stator cores and each phase winding is wound on a respective one of the stator cores. It is to be understood, however, that motors with a high number of stator core segments may have a plurality of core segment windings associated with respective phases.
A motor in accordance with the present invention may be under the control of motor energization circuitry that couples the stator windings to a source of power for supplying controlled energization current to the windings, the motor energization circuitry having a plurality of power output supply terminals fewer in number than the number of junctions. A central processor, coupled to the motor energization circuitry, performs appropriate control for motor winding energization. The motor energization circuitry may comprise a set of controlled switches connected to each power supply output terminal. Monitoring means are provided for monitoring the current in each of the plurality of stator phase windings and coupled to the central processor to provide current feedback signals.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.